The present invention relates to an electroluminescent (EL) device and apparatus. In particular, the present invention relates to a high luminance EL device and apparatus which present white appearances both in the light-emitting and non-light-emitting states.
EL devices are known, which comprise a semiconductor luminescent layer or a so-called xe2x80x9cdispersion type luminescent layerxe2x80x9d that is formed by dispersing luminescent particles such as fluorescent substances in a matrix resin such as a polymer having a high dielectric constant.
For example, an EL device comprising a xe2x80x9cdispersion type luminescent layerxe2x80x9d can be formed by laminating a transparent substrate, a transparent electrode layer, an insulating layer consisting of a matrix resin, a luminescent layer comprising a matrix resin and fluorescent particles, the same insulating layer as above, and a rear electrode in this order, as disclosed in JP-B-59-14878.
Japanese Patent Publication JP-B-62-59879 discloses an EL device comprising a polyester film, an ITO electrode, a luminescent layer comprising a matrix resin and fluorescent particles, and an aluminum foil (a rear electrode), which are laminated in this order.
Such the EL devices assume the color of light emitted from the fluorescent particles, and do not emit white light. Thus when a light-transmitting printed layer is provided on the light-emitting surface of the device, the printed colors cannot be highlighted as much as those printed on a white substrate.
Japanese Patent Publication JP-B-5- 17676 discloses an EL device comprising a dispersion type luminescent layer containing fluorescent particles which emit blue-green light and a pigment which emit fluorescent red light that is the complimentary color to the blue-green light, and thus emitting white light as a whole. However, this device assumes the red color of the pigment in the non-light-emitting state.
On the other hand, xe2x80x9cwhite EL devicesxe2x80x9d which assume the white appearances both in the light-emitting and non-light-emitting states are also known. For example, Japanese Patent Publications JP-A-63-19796 and JP-A-6-168784 disclose EL devices comprising an EL device having a dispersion type luminescent layer, and a white sheet being laminated on the light-emitting surface of the luminescent layer and allowing the transmission of diffused light. These devices present the white appearance both at the light-emitting and non-light-emitting states, since the luminescent layer emits white light, while the white sheet shields the color of EL devices in the non-light-emitting state.
However, the above white sheet has a transmission of 50% or less, and does not allow the light from the luminescent layer to pass through the sheet sufficiently. Thus, the luminance in the light-emitting state decreases.
The present invention provides an EL device which presents a white appearance in the non-light-emitting state, and emits white light with high luminance in the light-emitting state, so that colors of a light-transmitting printed layer, which is formed on the light-emitting surface of the EL device, are highlighted, and the problems of the above conventional techniques are solved.
Accordingly, to solve the above problems, one aspect of the present invention is an electroluminescent device comprising an electroluminescent element having a light-emitting surface, which emits white light, and a liquid crystal layer which is placed on said light-emitting surface, has a haze of 20% or less when a voltage is applied, and assumes a white color and has a haze of 70% or larger when no voltage is applied, wherein said device presents a white appearance both in the light-emitting and non-light-emitting states of the electroluminescence element, and an electroluminescent apparatus comprising a power source, (b) an electroluminescent element having a light-emitting surface which emits white light, and being electrically connected with said power source, and (c) a liquid crystal layer which is placed on said light-emitting surface, has a haze of 20% or less when a voltage is applied, and assumes a white color and has a haze of 70% or larger when no voltage is applied, and which is electrically connected with said power source, wherein said electroluminescence element and said liquid crystal layer are connected with said power source so that the voltage is applied to them at the same time.
According to the present invention, the liquid crystal layer, which is provided on the light-emitting surface of the EL device, shields the color-of EL device effectively and provides a good white appearance, since it assumes the white color when no voltage is applied and has a haze of at least 70%. Therefore, the colors of the light-transmitting printed layer formed on the light-emitting surface of the EL device can be highlighted.
The liquid crystal layer can allow the light to pass through the layer without decreasing the luminance of the EL device which emit white light, since its haze becomes 20% or less when the voltage is applied. Therefore, the colors of the printed layer can be highlighted in the light-emitting state of the EL device, as in the non-light-emitting state. Furthermore, the EL device can have the same appearance both in the light-emitting and non-light-emitting states.
Herein, the xe2x80x9chazexe2x80x9d of the liquid crystal layer is measured according to Japanese Industrial Standard JIS K 7105 6.2 using a color difference meter xe2x80x9cxcexa390xe2x80x9d manufactured by NIPPON DENSHOKU KABUSHIKIKAISHA.
The whiteness of the device can be effectively improved both in the light-emitting and non-light-emitting states, when the EL device comprises the luminescent layer and the color filter layer containing a colorant which emits a complimentary color to the color of light emitted by the luminescent layer, and the surface of the color filter layer forms the light-emitting surface.
Furthermore, the filling rate of the luminescent particles in the luminescent layer increases, and thus the luminance of the EL device is further improved, when the luminescent layer has the luminescent particle layer which substantially consists of particles including the luminescent particles, and is placed between the support layer and the insulating layer and in contact with both the support layer and the insulating layer.
The EL apparatus of the present invention comprises (a) a power source, (b) an electroluminescent element having a light-emitting surface which emits white light, and being electrically connected with said power source, and (c) a liquid crystal layer which is placed on said light-emitting surface, has a haze of 20% or less when a voltage is applied, and assumes a white color and has a haze of 70% or larger when no voltage is applied, and which is electrically connected with said power source, wherein said electroluminescence element and said liquid crystal layer are connected with said power source so that the voltage is applied to them at the same time.
Accordingly, the EL apparatus can have the white appearance both in the light-emitting state and non-light-emitting states.
Other features and advantages of the invention will be found in the discussion of the embodiments in reference to the following drawings.